Research On Preparation Of Thermochromic Fa(?)ade Materials And Their Utilizations In Buildings

With the increase in urbanization rate,people's demand for indoor thermal environment quality is increasing and building air conditioning energy consumption is rising.Using thermochromic coatings on building envelops is a promising method in reducing building air conditioning energy consumption and improving thermal environment of urbans.In this paper,thermochromic coatings in red color with different formulas are developed to determine the optimal formula.The results show that solar reflectance of the thermochromic coatings has the maximum change between colored phase and colorless phase when the mass fraction of TiO₂ is 10%,and when the content of TiO₂ is determined,the mass fraction of TCM has no significant effect on the reflectance.The investigation on the particle size of TiO₂ shows that solar reflectance has the most obvious variation when the particle size is 60nm.Thermochromic coatings with five different colors are prepared and their optical properties are analyzed.The change in solar reflectance between colored and colorless phases is 0.04-0.26 for the samples with 5wt%TiO₂ and 5 wt%TCM,and 0.07-0.3 for the samples with 10 wt%Ti O2and 5 wt%TCM.Outdoor measurements are carried out for thermochromic samples as well as common and cool coating samples and the results show that on warm sunny days,the temperature of thermochromic coatings is basically lower than the common coating;while on cold days,the temperature is higher than the common coating.Energy performance simulation is performed by Energy Plus using a two-story office building as an example.The simulation for thermochromic coatings uses a three-step control method based on their dynamic color-changing properties.It is observed that when the building is located in Shanghai,average daily temperature of building exterior surfaces using thermochromic coatings is lower compared to the common coating during cooling period and higher than the cool coating during heating period.Annual energy consumption results indicate that thermochromic coatings can avoid the penalty of increasing heating load for cool coatings.In particular,the annual energy consumption of the office building using thermochromic coatings can be reduced by 4.28-5.02 k Wh/m² compared to the common coating,and 0.73-1.47 k Wh/m² compared to the cool coating.While in Oslo whose heating demand is much more than cooling demand,the annual energy consumption can be reduced by 1.24-1.49k Wh/m² for thermochromic coatings compared to the common coating and0.12-0.37 k Wh/m² compared to the cool coating.Thermochromic coatings are more favorable in the areas which have both high cooling and heating demands.